DETERMINATION OF LC50 FROM DAPHNIA-MAGNA IN TREATED INDUSTRIAL-WASTE WATERS AND NON-TREATED HOSPITAL EFFLUENTS

The water flea Daphnia magna Straus is the most commonly used zooplank ton species in toxicological tests. This information has been used to set water quality criteria. In this paper, the proposed Mexican standa rd for waste water testing is described and results obtained from diff erent treated industrial waste waters and non-treated hospitals efflue nts by this method are presented. The results show that daphnids have a sensitivity close to that reported in the literature, since the LC50 determined for SDS is similar to previous results. Of the 10 industri al institutions tested, 5 discharged toxic effluents and the remaining 5 did not in terms of LC50. Of the 3 hospitals, 2 discharged toxic wa ters. Taking into account the 13 institutions, 2 of them discharge tox ic effluents of more than 230 ATU. The hardness and pH might contribut e to the lethality induced by some effluents but in others some toxic chemical could be present. Water treatment plants in operation in some of the companies did not work properly in 50% of the examined cases. (C) 1997 Elsevier Science Ltd.